Known in the art are some electric insulation materials based on cellulose and processes for producing thereof aimed at improving stabilization of tan .delta. and resistivity. Known processes comprise the stages of paper pulp preparation, sheet-making, pressing, and drying. A decrease in ionic dielectric losses is attained by introducing of chemical reagents into a paper pulp, (for instance, zinc salts (Inventor's Certificate of the USSR No. 540,003) and magnesium salts (Inventor's Certificate of the USSR No. 300562).
However, a decrease in tan .delta. of electric insulation material is observed only at elevated temperatures (80.degree.-140.degree. C.) and is very small at lowered temperature (30.degree.-80.degree. C.).
Also known in the art is electric insulation material based on a modified cellulose and process for preparing thereof.
As a modified cellulose use is made of borylated cellulose obtained by treating cellulose with a melt of a boric acid mixture with urea or borax at 180.degree.-260.degree. C. with subsequent water-washing of an unreacted boric acid (Inventor's Certificate of the USSR Nos. 303390 and 536275). The electric insulation material obtained by known method has decreased dipole dielectric losses, whereas ionic dielectric losses remain unchanged. In addition, this method is technologically complicated and does not find practical application.